Injector coking is a serious problem in direct injected internal combustion engines, because the injectors are in contact with the harsh environment of the combustion chamber. Because of the high temperatures, fuel decomposes in the injector nozzle and lays down a deposit which both restricts flow, and distorts the symmetry of the spray. As this deposit grows with operation, the internal dimensions of the nozzle change.
The buildup of deposits in the combustion chamber can alter engine performance by impairing fuel economy, regulated emissions, and driveability, and in the worst case scenario causing engine damage. A detailed account of such deposits, problems and some attempted solutions can be found in S.A.E. Technical Paper No. 902105 (1990) by G. T. Kalghatgi. Carbonaceous deposits are especially problematic for fuel injectors located within the engine combustion chamber. Direct injection spark ignition (DISI) engines include a fuel injector injecting fuel directly into the combustion chamber.
If the fuel injector could be made to resist the carbonaceous deposits, existing fuels and fuel injector designs could be utilized. In the past, components have been coated with amorphous hydrogenated carbon to increase hardness and durability, decrease friction and wear and protect against corrosion. As described in U.S. Pat. Nos. 5,249,554, 5,309,874, and 5,237,967 assigned to Ford Motor Company, and incorporated herein by reference, power train components have been coated with such carbon film coatings to reduce friction and wear related thereto. More recently, coatings have also been applied in an effort to reduce deposit formation. One example is U.S. Pat. No. 3,552,370, issued to Briggs et al, which describes a coating, and method of application, including the constituents of nickel, aluminum and copper for the purpose of reducing heat transfer from the combustion chamber to foster a more complete combustion.
Fuel additives alone typically are ineffective once fuel injectors have become fouled with substantial amounts of deposits such that the ability of the additive package to cleanse the injector is overcome.
Accordingly, there remains a need for fuel injectors that are capable of reducing and preventing the growth of carbonaceous deposits, especially so as to be able to keep deposits at a sufficiently low level that they may effectively be held at operable levels by fuel additives.